Dock levelers or dock boards are mounted on loading docks and are adapted to bridge the gap between the dock and the bed of a truck or carrier parked in front of the dock to enable material handling equipment, such as a forklift truck to move between the dock and the truck bed.
The typical dock leveler includes a frame or supporting structure which is mounted in a pit or depression in the loading dock and the rear end of a ramp or deck plate is pivoted to the supporting structure so that the ramp is movable between a horizontal cross traffic position and an upwardly inclined position.
Hinged to the forward end of the ramp is an extension lip which is movable between a downwardly hanging pendant position and an extended position where the lip forms an extension to the ramp.
After a truck has parked in front of the loading dock in preparation for a loading operation, the ramp of the conventional dock leveler is pivoted upwardly and as the ramp approaches its upwardly inclined position, the lip is pivoted outwardly to the extended position. As the ramp is subsequently lowered, the extended lip will engage the bed of the truck. After the loading operation has been completed, the lip will fall by gravity to the pendent position as the truck pulls away from the loading dock.
Traditionally, the ramp of the dock leveler has been operated either by a mechanical or hydraulic mechanism. With a typical mechanical operation, an extension spring is mounted in the pit beneath the ramp and is connected through a lever arm to the rear edge of the ramp. When a ramp holddown mechanism is released, the force of the spring will pivot the ramp to the upwardly inclined position.
With a hydraulically-operated dock leveler, a hydraulic cylinder unit is connected between the supporting frame and the ramp and through extension of the cylinder unit, the ramp will be pivoted to the upwardly inclined position.
U.S. patent application Ser. No. 07/814,002, filed Dec. 26, 1991, now abandoned, describes an inflatable bag mechanism that is utilized to pivot the ramp to the upwardly inclined position. As described in that patent application, a pleated bag is interposed between the bottom of the pit in the loading dock and the undersurface of the ramp. By inflating the bag with low pressure air, the ramp will be pivoted to the upwardly inclined position.